Allograft intervertebral implant and method of manufacturing the same

ABSTRACT

The present invention is directed to an allograft intervertebral implant sized and configured for insertion between adjacent vertebral bodies in a spinal fusion surgery. The implant is preferably manufactured from two or more pieces of allograft bone joined together by a joint, more preferably a dovetail joint. The dovetail joint being sized and configured to substantially follow the exterior shape or surface of the intervertebral implant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/633,333 filed Oct. 2, 2012, which is a continuation of U.S. patentapplication Ser. No. 13/359,674, filed Jan. 27, 2012, now U.S. Pat. No.8,460,389, which is a continuation of U.S. patent application Ser. No.11/854,132, filed Sep. 12, 2007, now U.S. Pat. No. 8,128,700, whichclaims the benefit of U.S. Provisional Application No. 60/844,515, filedSep. 13, 2006, which are all incorporated by reference herein in theirentireties for all purposes.

FIELD OF INVENTION

The present invention is directed to an intervertebral implant, moreparticularly to an intervertebral implant made from two or more piecesof allograft bone.

BACKGROUND

A number of medical conditions such as, for example, compression ofspinal cord nerve roots, degenerative disc disease, herniated nucleuspulposus, spinal stenosis and spondylolisthesis can cause severe backpain. Intervertebral fusion is one surgical method for alleviating backpain. In a posterior lumbar interbody fusion (“PLIF”) procedure, twoadjacent vertebral bodies are fused together by removing the affectedintervertebral disc and inserting posteriorly one or more implants oneither side of the midline of the spine that would allow for bone togrow between the two adjacent vertebral bodies to bridge the gap left bythe removed intervertebral disc.

One variation to the traditional PLIF technique is a transforaminalposterior lumbar interbody fusion (“T-PLIF”) procedure. Pursuant to thisprocedure, an implant is inserted into the affected disc space via aunilateral (or sometimes bilateral), posterior approach, offset from themidline of the spine, by removing portions of the facet joint of thevertebrae. The T-PLIF procedure avoids damage to nerve structures suchas the dura, cauda equina and the nerve root, but the resultingtransforaminal window available to remove the affected disc, prepare thevertebral endplates, and insert the implant is limited laterally by softtissue and medially by the cauda equina.

A number of different implants have been specifically developed for usein connection with the PLIF and T-PLIF procedures with varying success.These include titanium or polymer cages and allograft solid bodies. Forexample, U.S. Pat. No. 6,719,794 to Gerber et al. discloses, inter alia,an intervertebral implant for use in aT-PLIF procedure made from one ormore pieces of allograft bone. The multi-piece implant is joinedtogether by a plurality of interlocking surfaces. The implant mayfurther include one or more pins for securing the implant together.However, because of the interlocking surfaces and pins, theintervertebral implant is formed as a solid body implant (e.g., theimplant does not contain any through bore for receiving bone graftmaterial). That is, because of the complexities of forming and machiningimplants from allograft bone as compared to forming and machiningimplants from a metal, polymer, etc., manufacturers have been unable tomanufacture implants sized and configured for PLIF and T-PLIF proceduresthat include one or more through bores for receiving bone graft materialto facilitate bone fusion.

Moreover, known multi-piece allograft implants are generally initiallyjoined together and then the joined pieces are shaped, this may resultin less control and in reduced size potential.

There is a need for an improved intervertebral implant made frommultiple pieces of allograft bone, wherein the pieces are joinedtogether to enable the implant to remain assembled in situ, structurallysupport the required spinal loads and preferably to also contain one ormore through-bores for receiving bone graft material to facilitate bonefusion of the adjacent vertebrae bodies.

SUMMARY

The present invention is directed to an intervertebral implant sized andconfigured for insertion between adjacent vertebral bodies in a spinalfusion surgery. The implant is preferably manufactured from two or morepieces of allograft bone joined together by a dovetail joint. Thedovetail joint being sized and configured to substantially follow theexterior shape or surface (e.g. perimeter) of the intervertebralimplant. The dovetail joint may preferably follow a curved surface orline, for example, the dovetail joint preferably follows the contours ofthe curved front and back surfaces of the implant. The intervertebralimplant may also include one or more bone pins for joining the allograftpieces, the pins being inserted into the implant at an anglesubstantially vertical and/or perpendicular with respect to theinterfacing surface of the dovetail joint. The intervertebral implantmay also include one or more central through-bores for receivingostegenic or bone graft material. The intervertebral implant ispreferably sized and configured for insertion in a T-PLIF or PLIFprocedure.

In one exemplary embodiment, the intervertebral implant is sized andconfigured for implantation between first and second adjacent vertebravia a transforaminal lumbar interbody fusion technique. The implantincluding an allograft body formed from at least two pieces of allograftbone, the body including a curved front surface, a curved back surface,a pair of ends, preferably curved ends, separating the curved front andback surfaces, an upper surface and a lower surface. The upper and lowersurfaces preferably being sized and configured for contacting at least aportion of the first and second vertebrae. The curved front and backsurfaces preferably defining an outer perimeter of the implant. The atleast two pieces of allograft bone are preferably joined together by adovetail joint, the dovetail joint having a curved shape thatsubstantially follows the contours of the curved front and backsurfaces. The dovetail joint may also substantially follow the contoursof one of the ends of the implant.

The at least two pieces of allograft bone may each include a hole atleast partially formed therein, the hole being sized and configured toreceive at least one pin for further securing the pieces of allografttogether. The pins being substantially vertical and/or perpendicularwith respect to the interfacing surface of the dovetail joint.

The implant further including at least one through-bore extending fromthe upper surface to the lower surface, the through-bore being sized andconfigured to receive bone grafting material for facilitating spinalfusion.

In another exemplary embodiment, the intervertebral implant may be sizedand configured for implantation between first and second adjacentvertebra via a posterior lumbar interbody fusion procedure. The implantincluding an allograft body formed from at least two pieces of allograftbone, the body including an anterior surface, a posterior surface, apair of lateral side surfaces, an upper surface and a lower surface. Theupper and lower surfaces being sized and configured for contacting atleast a portion of the first and second vertebrae. The at least twopieces of allograft bone preferably being joined together by at leastone dovetail joint, the at least one dovetail joint being orientatedsubstantially transverse to a longitudinal axis of the implant.

The at least two pieces of allograft bone may each include a hole atleast partially formed therein, the hole being sized and configured toreceive at least one pin for further securing the pieces of allografttogether. The pins being substantially vertical and/or perpendicularwith respect to the interfacing surface of the dovetail joint.

The implant further including at least one through-bore extending fromthe upper surface to the lower surface, the through-bore being sized andconfigured to receive bone grafting material for facilitating spinalfusion.

The present invention is further directed to a method for manufacturingan allograft implant from two or more individual pieces. The methodpreferably including the steps of: (a) obtaining one or more pieces ofallograft bone, (b) shaping the individual implant pieces out ofallograft bone into their desired shaped, the desired shape includingforming one of either the recess or projection portion of a dovetailjoint, and (c) joining the individual pieces together by sliding theindividual members together via the dovetail joint. Forming the portionsof the dovetail joint may include forming one or more of either therecess or projection portion of the dovetail joint in a single piece,the recess or projection portion may be formed in more than one surface.The method may further include removing the individual pieces from theallograft bone. The method may further include the steps of forming oneor more holes preferably through holes into one or more of theindividual pieces, the holes being sized and configured to receive bonepins. The method may also include forming one or more through-bores intothe implant for receiving bone graft material for facilitating spinalfusion. The step of forming the holes and/or through-bore may occureither before or after the individual pieces have been joined together.

BRIEF DESCRIPTION OF THE DRAWINGS

The system is explained in even greater detail in the followingexemplary drawings. The drawings are merely exemplary to illustrate thestructure of preferred devices and certain features that may be usedsingularly or in combination with other features. The invention shouldnot be limited to the embodiments shown.

FIG. 1A is a perspective view of an exemplary embodiment of a T-PLIFimplant;

FIG. 1B is a partial top view, partial cross-sectional view of theT-PLIF implant shown in FIG. 1A;

FIG. 1C is a cross-sectional of the T-PLIF implant shown in FIG. 1A;

FIG. 2A is another perspective view of an exemplary embodiment of aT-PLIF implant;

FIG. 2B is a top view of an exemplary embodiment of a T-PLIF implantshown in FIG. 2A;

FIG. 2C is a perspective view depicting the first and second members ofthe exemplary embodiment of the T-PLIF implant shown in FIG. 2A;

FIG. 2D is another perspective view depicting the first and secondmembers of the exemplary embodiment of the T-PLIF implant shown in FIG.2A;

FIG. 3A is a perspective view of an exemplary embodiment of a secondmember of an exemplary embodiment of a T-PLIF implant;

FIG. 3B is a perspective view of an exemplary embodiment of a firstmember of an exemplary embodiment of a T-PLIF implant;

FIG. 3C is another perspective view of the second member shown in FIG.3A;

FIG. 4A is a perspective view of another exemplary embodiment of aT-PLIF implant;

FIG. 4B is a cross-sectional view of the T-PLIF implant shown in FIG.4A;

FIG. 5 is a schematic representation of another exemplary embodiment ofa T-PLIF implant;

FIG. 6A depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6B depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6C depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6D depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6E depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6F depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6G depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6H depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6I depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 6J depicts one or more steps for manufacturing an exemplaryembodiment of a T-PLIF implant in accordance with one aspect of thepresent invention;

FIG. 7 is a perspective view of an exemplary embodiment of a PLIFimplant;

FIG. 8A is another perspective view of the PLIF implant shown in FIG. 7;

FIG. 8B is another perspective view of the PLIF implant shown in FIG. 7;

FIG. 8C is a perspective view depicting the first and second members ofthe PLIF implant shown in FIG. 7;

FIG. 9A is a perspective view of an exemplary embodiment of a PLIFimplant;

FIG. 9B is a top view of the PLIF implant shown in FIG. 9A; and

FIG. 9C is a side view of the PLIF implant shown in FIG. 9A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Certain exemplary embodiments of the invention will now be describedwith reference to the drawings. In general, such embodiments relate toan intervertebral implant for insertion between adjacent vertebralbodies to restore vertebrae spacing wherein the implant is sized andconfigured for use as an intervertebral spacer in a spinal fusionsurgery, wherein an affected disk is removed from between two adjacentvertebrae and replaced with the implant. The implant preferably providessegmental stability and allows for bone to grow in-between the twoadjacent vertebrae to bridge the gap created by disk removal. By way ofnon-limiting example, the intervertebral implant may be made from two ormore pieces of allograft bone. The invention may have other applicationsand uses and should not be limited to the structure or use described andillustrated. As will be described in greater detail below, theintervertebral implant may include two or more pieces of allograft bonejoined together by way of, for example, a dovetail joint. Preferably, aswill be described in greater detail below, the dovetail joint is sizedand configured to substantially follow at least a portion of theexterior shape or surface (e.g. perimeter) of the intervertebralimplant. For example, the dovetail joint is preferably sized andconfigured to substantially follow two or three surfaces of the implantsuch as, for example, the curved front and back surfaces of the implantor the curved front and back surfaces and one of the end surfaces of theimplant. The intervertebral implant may also include one or more bonepins for joining the allograft pieces. The intervertebral implant mayalso include one or more through-bores for receiving ostegenic or bonegraft material. The intervertebral implant is preferably sized andconfigured for insertion during a T-PLIF procedure. Alternatively, theintervertebral implant may be sized and configured for insertion duringa PLIF procedure.

In FIGS. 1A-1C an exemplary embodiment of aT-PLIF implant 10 is shown.The T-PLIF implant 10 may include a curved body 20. The body 20 mayinclude a curved front surface 22, a curved back surface 24, a pair ofnarrow ends 26, 28 separating the curved front and back surfaces 22, 24,an upper surface 30 and a lower surface 32. The upper and lower surfaces30, 32 are preferably sized and configured to contact at least a portionof the endplates of the adjacent vertebral bodies. Alternatively, theT-PLIF implant 10 may take on various other profiles and exteriorgeometries, depending on the area of the spine to be treated. The curvedfront and back surfaces 22, 24 facilitate the offset insertion of theT-PLIF implant 10 through the narrow transforaminal window and into thedisk space. The narrow ends 26, 28 may be rounded (as shown) or blunt.The upper and lower surfaces 30, 32 may include projections 33, such as,for example, a plurality of teeth 34 for engaging the adjacentvertebrae. The projections 33 formed on the upper and lower surfaces 30,32 preferably provide a mechanical connection between the T-PLIF implant10 and the end plates by penetrating at least a portion of the endplates. The initial mechanical stability afforded by incorporation ofthe projections 33, and in particular the teeth 34, minimizes the riskof post-operative expulsion and/or slippage of the T-PLIF implant 10. Itshould be noted that the T-PLIF implant 10 may include other forms ofprojections 33 aside from teeth 34 including, for example, ridges,grooves, threads, etc.

The T-PLIF implant 10 may also include one or more channels 36.Preferably, the channel 36 extends from one of the ends 26,28 of theT-PLIF implant 10 (shown as end 26). The channel 36 is preferably sizedand configured to engage a surgical instrument, such as an implantholder. Preferably, the T-PLIF implant 10 is formed with at least twochannels 36, one on each of the front and back surfaces 22, 24. Thechannels 36 being sized and configured with a curved surface tosubstantially follow the curved surfaces of the front and back surfaces22, 24. It should be noted however that the T-PLIF implant 10 may beconfigured with a single channel 36 formed on only one of the surfaces22, 24 thereof. Alternatively, the channel 36 may be formed on the upperand/or lower surfaces 30, 32 of the T-PLIF implant 10, or any othersurface thereof. Alternatively, the T-PLIF implant 10 may be configuredwithout channels altogether. Other methods for engaging the T-PLIFimplant 10 with surgical instruments, such as a threaded hole forreceiving the threaded end of a surgical tool or a non-threaded hole forreceiving an expandable head of an insertion tool, may also be used.

As shown in FIGS. 2A-2D, the T-PLIF implant 10 may be constructed fromtwo or more pieces. This multi-piece configuration may be particularlyuseful for implants formed of allograft bone, since it may be difficultand/or impractical to obtain a single, sufficiently large piece ofallograft for some applications. The T-PLIF implant 10 may be formed bya first member 50 and a second member 80. Although the T-PLIF implant 10may be formed from more or less pieces. The first member 50 may bejoined to the second member 80 by any means. Preferably, the firstmember 50 is joined to the second member 80 by a dovetail joint.

As best shown in FIGS. 3A-3C, the first member 50 may include a recess55 formed therein, the recess 55 being sized and configured to receive aprojection 82 formed on and extending from the second member 80. Therecess 55 and projection 82 may take on any form. For example, theprojection 82 may include a base surface 83, two outwardly tapered sidesurfaces 84, 85 extending from the base surface 83 and a substantiallyplanar surface 86. As shown, the cross sectional area of the projection82 may become larger as the distance of the projection 82 from the basesurface 83 increases. The recess 55 similarly may include a base surface55 a and two inwardly tapered side surfaces 56, 58 extending from thebase surface 55 a. As shown, the cross sectional area of the recess 55may become smaller as the distance of the recess 55 from the basesurface 55 a increases. The size and configuration of the taperedsurfaces 56, 58 formed on the first member 50 being sized and configuredto receive the tapered side surfaces 84, 85 of the projection 82 sothat, as will be generally appreciated by one of ordinary skill in theart, a dovetail joint is formed. The dovetail joint enables the firstand second members 50, 80 to slide with respect to one another,preferably the first and second members 50, 80 slide substantially alongthe longitudinal axis 11 of the implant 10, while substantiallyresisting the first and second members 50, 80 from verticallyseparating.

More preferably, the recess 55 and the projection 82, and hence thedovetail joint, are formed so that they have a curved shape thatsubstantially corresponds with the curved shape of the T-PLIF implant10. Preferably, the dovetail joint has a curved surface thatsubstantially follows, at least, the contours of the curved front andback surfaces 22, 24. As shown in FIG. 3B, the inwardly tapered surfaces56, 58 of the recess 55 may be machined in the first member 50 along thefront surface 22, the back surface 24, and one of the narrow ends (shownhere as 28). The recess 55 may be opened at one of the narrow ends(shown here as 26) thus forming an entry space 59 for slidably receivingthe projection 82. In this manner, the recess 55 can slidably receivethe projection 82 formed on the second member 80 along the longitudinalaxis 11 of the implant 10.

The entry space 59 may be formed with a slightly larger opening tofacilitate easier insertion of the projection 82 into the recess 55. Therecess 55 may become more narrow towards the rear of the dovetail joint(towards end 28) so that the first and second members 50, 80 can be slidtogether easily but the dovetail joint becomes tighter as its finalposition is reached. Alternatively, the recess 55 may have the samedimension throughout. Preferably, the first and second members 50, 80are sized and configured within sufficient tolerance so that once theprojection 82 is fully inserted into the recess 55 the first and secondmembers 50, 80 resist separation of the first and second members 50, 80.That is, the first and second members 50, 80 may be sized and configuredso that when the projection 82 is fully inserted into the recess 55, apress-fit type connection is achieved. While it has been described andshown as if the projection 82 is slidably receivable within the recess55 via one of the narrow ends 26, 28 it should be understood that theprojection 82 may be slidably receivable into the recess 55 via one ofthe front and/or back surfaces 22, 24, or any other surface thereof.

The second member 80 is preferably sized and configured so that oncefully inserted into the first member 50, the outer surface of theimplant 10 is substantially smooth and devoid of any gap formed by thedovetail joint. For example, the second member 80 may include a ledge 88(as best shown in FIG. 2D) formed on an end thereof, the ledge 88 beingsized and configured to cover the entry space 59 of the recess 55.

The T-PLIF implant 10 may also include one or more pins 62 for securingthe first and second members 50, 80, as best shown in FIGS. 2A-2D. Thepins 62 may take on any configuration including but not limited tocircular, elliptical, oval, square, rectangular, star shaped, etc. Thepins 62 may be secured within the implant 10 in a variety of ways,preferably, the T-PLIF implant 10 may include one or more holes 64 forreceiving the pins 62. The pins 62 and respective holes 64 may be sizedso that they extend from the upper surface 30 to the lower surface 32.Alternatively, the pins 62 and respective holes 64 may be sized so thatthey extend only through a portion of the height of the implant 10. Thepins 62 may be secured within the corresponding holes 64 by any meansincluding but not limited to press-fit, adhesive, mechanical connectionsuch as, for example, threaded connection, etc.

The T-PLIF implant 10 may incorporate substantially straight pins 62.More preferably, by incorporating a joint, such as, for example, adovetail joint that resists vertical separation of the first and secondmembers with respect to one another, the pins 62 may extendsubstantially vertical and/or perpendicular with respecting to theinterfacing surface of the joint. The pins 62 may intersect theinterfacing surface of the joint at an angle {acute over (ω)},preferably at a substantially ninety-degree angle with respect to theinterfacing surface of the joint. The incorporation of substantiallystraight vertical pins 62 facilitates maximum resistance against thefirst and second members 50, 80 from sliding apart and enables one ormore vertical throughbores 60 to be formed in the implant 10, thethrough-bore 60 being sized and configured to receive bone graftmaterial to facilitate bone fusion of the adjacent vertebrae bodies.Preferably, the implant 10 includes at least two substantially straightvertical pins 62, one on either side of the through-bore 60, adjacentthe ends 26, 28 of the implant 10. Preferably, the pins 62 will be asfar apart as possible to maximize the size of the vertical through-bore60. A larger through-bore 60 may allow the surgeon to pack additionalbone graft and other bone growth inducing material into the implant 10.It should be understood however that the number, location and/ororientation of the pins 62 can be varied, for example, one, three ormore pins 62 may also be used. Additionally, the pins 62 may be placedobliquely or at an angle with respect to the interfacing surface of thejoint.

The T-PLIF implant 10 may alternatively include two or more verticalthrough-bores 60 extending from the upper surface 30 to the lowersurface 32 of the implant 10. Alternatively and/or in addition, theT-PLIF implant 10 may include one or more horizontal bores (not shown).The horizontal bores may extend from the back surface 22 to the frontsurface 24 or from one or both of the ends 26, 28. Alternatively, theimplant 10 may not include any bores, vertical or horizontal.

While the T-PLIF implant 10 has been generally described asincorporating a first member 50 and a second member 80, wherein thefirst and second members 50, 80 are located one on top of the other, itshould be understood that, as best shown in FIGS. 4A and 4B, the firstand second members 50, 80 may be arranged in a side by sideconfiguration. As shown in this configuration, the T-PLIF implant 10 mayinclude a substantially straight dovetail configuration extending fromthe upper surface 30 to the lower surface 32. Moreover, as best shown inFIG. 4B the pins 62 may be generally oriented perpendicular to thedovetail joints. Alternatively, the pins 62 may be oriented at an acuteangle δ with respect to the longitudinal axis 11 of the implant 10.

While the T-PLIF implant 10 has been described as being formed fromfirst and second members 50, 80, it should be understood that the T-PLIFimplant 10 may include three or more pieces and/or members. As bestshown in FIG. 5, for example, the T-PLIF implant 100 may be formed froma first member 130, a second member 135 and a third member 140. As bestshown in FIGS. 6G-6J, the first and second members 130, 135 may beformed with projections 82, while the third member 140 may be formedwith a pair of recesses 55 for engaging the projections 82 formed on thefirst and second members 130, 135. Alternatively, the third member 140may be formed with a pair of projections 82 and the first and secondmembers 130, 135 may be formed with recesses 55 for securing theprojections 82. Alternatively, the third member 140 may be formed withboth a projection 82 and a recess 55 while one of the first and secondmembers 130, 135 may be formed with a recess 55 for engaging theprojection 82 formed on the third member 140. The other of the first andsecond members 130, 135 being formed with a projection 82 for engagingwith the recess 55 formed on the third member 140. The orientation ofthe members may be provided in any appropriate combination.

The dimensions of the T-PLIF implant 10 can be varied to accommodate apatient's anatomy. For example, the length of the T-PLIF implant 10, asgenerally measured by the distance between the ends 26, 28 of theimplant 10, may range from about 26 mm to about 33 mm. The width of theT-PLIF implant 10, as generally measured by the distance between thefront and back surfaces 22, 24, may range from about 9 mm to about 12mm. Through a combination of implants, it is envisioned that implantshaving footprints of, for example, 10 mm×27 mm, 10 mm×30 mm, 10 mm×33mm, 12 mm×27 mm, 12 mm×30 mm, and 12 mm×33 mm may be possible.

The height of the T-PLIF implant 10, as generally measured as thedistance between the upper and lower surfaces 30, 32 of the implant 10,is generally chosen based on the size of the disk space to be filled.Preferably, the height of the T-PLIF implant 10 is greatest at themidsection between the two narrow ends 26, 28 and tapers gradually alongthe longitudinal axis 11 of the implant 10 so that it is thinnest at thenarrow ends 26, 28 of the implant 10. The taper is preferably curved andprovides a convex configuration for a better anatomical fit, while alsofacilitating insertion of the implant 10 into the affected disc space.The T-PLIF implant 10 may have a height at its mid-section of about 7.0mm to about 17.0 mm. The height at the ends 26, 28 of the T-PLIF implant10 may range from about 1.5 mm to about 2.0 mm less than the height atthe mid-section. Alternatively, the height of the T-PLIF implant 10 mayremain substantially constant throughout the implant 10. The height ofthe T-PLIF implant 10 preferably does not taper or change along theshorter axis 12 (e.g. axis transverse to the longitudinal axis 11) ofimplant 10. Thus for any given cross section taken perpendicular to thelongitudinal axis 11 of the implant 10, the distance between the upperand lower surfaces 30, 32 remains substantially constant. Alternatively,the height of the implant 10 may change or taper along the shorter axis12 of implant 10.

In one exemplary embodiment, the T-PLIF implant 10 may be about 30 mm inlength. The radius of curvature of the front surface 22 may be about 19mm. The radius of curvature for the back surface 24 may be about 29 mm.The length of the through-bore 60 may be about 15.5 mm. The lengthbetween the holes 64 may be about 20 mm. The diameter of the holes 64may be about 2.4 mm. These dimensions are not to be construed so as tolimit the embodiments discussed above but rather to serve asillustrative examples of possible sizes of these various components.

As generally shown and described in U.S. Pat. No. 6,719,794 entitledIntervertebral Implant for Transforaminal Posterior Lumbar InterbodyFusion Procedure; U.S. Pat. No. 6,974,480 entitled IntervertebralImplant for Transforaminal Posterior Lumbar Interbody Fusion Procedure;U.S. Pat. No. 7,223,292 entitled Intervertebral Implant forTransforaminal Posterior Lumbar Interbody Fusion Procedure, U.S. Pat.No. 7,226,483 entitled Method of Performing a Transforaminal PosteriorLumbar Interbody Fusion Procedure, U.S. patent application Ser. No.10/787,984 entitled Intervertebral Implant for Transforaminal PosteriorLumbar Interbody Fusion Procedure and U.S. patent application Ser. No.11/745,293 entitled Intervertebral Implant for Transforaminal PosteriorLumbar Interbody Fusion Procedure, the entire contents of which are allexpressly incorporated by reference, the T-PLIF implant is preferablysized and configured for insertion in-between adjacent vertebra via aT-PLIF procedure which generally involves a posterior approach, offsetfrom a midline of the spine, to the affected intervertebral disk space.

In one exemplary T-PLIF procedure, a narrow transforaminal window may beproduced to permit insertion of the T-PLIF implant. The transforaminalwindow is generally limited laterally by the patient's dura and thesuperior exiting nerve root. In use, the T-PLIF procedure enables theT-PLIF implant to be seated in the disc space behind the dura withoutdisturbing the anterior curtain of the disc space. One exemplarysurgical technique for the T-PLIF procedure begins with the patientbeing placed in a prone position on a lumbar frame. Next, radiographicequipment may be used to assist the surgeon in locating the preciseintraoperative position for the T-PLIF implant. Next, an incision may bemade. Following incision, the facets, lamina and other anatomicallandmarks are identified. The affected vertebrae are then preferablydistracted using a lamina spreader or a lateral distractor, both ofwhich are commonly known in the art.

Following distraction, the transforaminal window is preferably createdby removing the inferior facet of the cranial vertebrae and the superiorfacet of the caudal vertebrae using, for example, one or moreosteotomes. A discectomy may then be performed during which a portionof, substantially all of, and more preferably all, of the disc materialfrom the affected disc space may be removed using a combination ofstraight and angled curettes. After the discectomy is complete, thesuperficial layers of the entire cartilaginous endplates may be removedwith a combination of straight and angled bone rasps. This is done toexpose bleeding bone, but care should be taken to avoid excess removalof subchondral bone, as this may weaken the anterior column. Entireremoval of the endplate may result in subsidence and loss of segmentalstability.

Next, an appropriately sized trial-fit T-PLIF spacer may be insertedinto the intervertebral disc space using gentle impaction, to determinethe appropriate height of the T-PLIF implant for the disc space to befilled. Fluoroscopy can assist in confirming the fit of the trialspacer. Upon identifying and removing the best fitting trial spacer, aT-PLIF implant of appropriate size is selected.

At this time, prior to placement of the T-PLIF implant, bone graftmaterial, such as autogenous cancellous bone or a bone substitute, maybe placed in the anterior and lateral aspects of the affected discspace. Moreover, since the T-PLIF implant is preferably formed with athrough bore, bone graft material may be inserted into the through-bore.Alternatively, the T-PLIF implant may come pre-arrived with bone graftmaterial packed therein.

During insertion, the T-PLIF implant may be held securely using asurgical instrument such as an implant holder, which may engage thechannels formed in or other features in the T-PLIF implant. The tips ofthe implant holder may be curved or angled to mate with the curvedimplant and to facilitate insertion of the implant into the disc space.The T-PLIF implant may then be introduced into the intervertebral discspace via the transforaminal window.

A guide tool having a curved blade which preferably matches thecurvature of the anterior face of T-PLIF implant may be used to properlyguide the T-PLIF implant into the affected disc space. Slight impactionmay also be necessary. Once the T-PLIF implant is in the desired finalposition, the implant holder and optional guide tool are removed andadditional bone graft material may be inserted in the anterior andlateral aspects of the affected disc space. Preferably, the T-PLIFimplant should be recessed from the anterior edge of the vertebral body.Moreover, preferably the curvature of the anterior face of the implantis substantially the same as the curvature of the anterior edge of thedisc space.

Alternatively, the intervertebral implant may be sized and configuredfor insertion during a PLIF procedure. As best shown in FIG. 7, the PLIFimplant 200 may include a body 210, the body 210 may include an anteriorsurface 260, a posterior surface 280, a pair of lateral side surfaces220, 240, an upper surface 300 and a lower surface 320. The upper andlower surfaces 300, 320 are preferably sized and configured to contactat least a portion of the endplates of the adjacent vertebral bodies.Alternatively, the PLIF implant 200 may take on various profiles andexterior geometries, depending on the area of the spine to be treated.The upper and lower surfaces 300, 320 may include projections 340, suchas, for example, a plurality of teeth 342 for engaging the adjacentvertebrae. The projections 340 formed on the upper and lower surfaces300, 320 preferably provide a mechanical connection between the PLIFimplant 200 and the end plates by penetrating at least a portion of theend plates. The initial mechanical stability afforded by incorporationof the projections 340, and in particular the teeth 342, minimizes therisk of post-operative expulsion and/or slippage of the PLIF implant200.

The PLIF implant 200 may also include one or more channels 360.Preferably, the channels 360 are formed in one or both of the lateralside surfaces 220, 240 and extend from the posterior surface 280 of theT-PLIF implant 200. The channel 360 is preferably sized and configuredto engage a surgical instrument, such as an implant holder. Preferably,the PLIF implant 200 is formed with at least two channels 360, one oneach of the lateral side surfaces 220, 240. It should be noted howeverthat the PLIF implant 200 may be configured with a single channel 360formed on only one surface thereof. Alternatively, the channel 360 maybe formed on the upper and/or lower surfaces 300, 320 of the PLIFimplant 200, or any other surface thereof. Alternatively, the PLIFimplant 200 may be configured without channels altogether. Other methodsfor engaging the PLIF implant 200 with surgical instruments, such as,for example, a threaded hole for receiving the threaded end of asurgical tool or a non-threaded hole for receiving an expandable head ofan insertion tool, may also be used.

The PLIF implant 200 may be constructed from two or more pieces. Thismulti-piece configuration may be particularly useful for implants formedof allograft bone, since it may be difficult and/or impractical toobtain a single, sufficiently large piece of allograft for someapplications. The PLIF implant 200 may be formed by a first member and asecond member. The first member may be joined to the second member byany means. Preferably, the first member is joined to the second memberby a dovetail joint. Alternatively, the PLIF implant 200 may containmore or less pieces and/or members. For example, as best shown in FIGS.8A-8C and 9A-9C, the PLIF implant 200 may be formed by a first member500, a second member 600 and a third member 700. The second member 600may be joined to the first and third members 500, 700 by any means.Preferably, the second member 600 is joined to the first and thirdmembers 500, 700 by dovetail joints.

As shown, the first, second and third members 500, 600, 700 may eachinclude one or more projections 820, one or more recesses 550, and/orone or more projections 820 and recesses 550 for interconnecting withone another. Any combination of recesses 550 and projections 820 may beused. The recess 550 and projection 820 may take on any form. Forexample, the recess 550 may include two inwardly tapered side surfacesfor slidably receiving two outwardly tapered side surfaces formed on theprojection 820, as previously described in connection with the T-PLIFimplant 10.

As shown, preferably the dovetail joint is sized and configured topermit the first, second and third members 500, 600, 700 to slide withrespect to one another substantially along an axis 202 transverse to thelongitudinal axis 201 of the implant 200, while substantially resistingthe members 500, 600, 700 from vertically separating. Alternatively, thePLIF implant 200 may include a dovetail configuration that substantiallyfollows the contours of the body 210, for example, the contours of thelateral sides surfaces 220, 240, of the PLIF implant 200 as describedabove in connection with the T-PLIF implant 10.

The PLIF implant 200 may also include one or more pins 620 (similar topins 62 described above) for further securing the first, second andthird members 500, 600, 700 together. The PLIF implant 200 mayincorporate substantially straight pins 620. More preferably, byincorporating a joint, such as, for example, a dovetail joint thatresists vertical separation of the first, second and third members 500,600, 700 with respect to one another, the pins 620 may extendsubstantially vertical and/or perpendicular with respect to theinterfacing surface of the joint. The pins 620 may intersect theinterfacing surface of the joint at an angle {acute over (ω)},preferably at a substantially ninety-degree angle with respect to theinterfacing surface of the joint. The incorporation of substantiallystraight vertical pins 620 facilitates maximum resistance against thefirst, second, and third members 500, 600, 700 from sliding apart andenables one or more vertical through-bores 900 to be formed in theimplant 200, the bore 900 being sized and configured to receive bonegraft material to facilitate bone fusion of the adjacent vertebraebodies. Preferably, the implant 200 includes at least one substantiallystraight pin 620. The pin can be located anywhere on the implant 200.Preferably, the pin 620 will be located so as to maximize the size ofthe vertical through-bore 900. A larger through-bore 900 may allow thesurgeon to pack the PLIF implant 200 with more bone graft and other bonegrowth inducing material. As shown, the pin 620 may be located near theanterior surface 280 of the implant 200. The number, location and/ororientation of the pins 620 can be varied, for example, two or more pins620 may be used. Additionally, the pins 62 may be placed obliquely or atan angle with respect to the interfacing surface of the joint.

The PLIF implant 200 may alternatively include two or more verticalthrough-bores 900 extending from the upper surface 300 to the lowersurface 320 of the implant 200. Alternatively, and/or in addition, thePLIF implant 200 may include one or more horizontal bores (not shown).The horizontal bores may extend from one or both of the lateral sidesurfaces 220, 240 or from one or both of the posterior and anteriorsurfaces 260, 280. Alternatively, the implant 200 may not include anythrough bores, either vertical or horizontal.

The dimensions of the PLIF implant 200 can be varied to accommodate apatient's anatomy. For example, the length of the PLIF implant 200, asgenerally measured by the distance from the anterior surface to theposterior surface, may range from about 18 mm to about 32 mm. The widthof the PLIF implant 200, as generally measured by the distance betweenthe two lateral side surfaces, may range from about 6 mm to about 14 mm.Through a combination of multiple piece design implants havingfootprints, for example, 6×18 mm, 14×32 mm, etc. may be possible.

The height of the PLIF implant 200, as generally measured by thedistance between the upper and lower surfaces, is generally chosen basedon the size of the disk space to be filled. Preferably, the height ofthe PLIF implant 200 is greatest at the a point in between themidsection and the anterior surface 260 and tapers gradually along thelongitudinal axis 201 of the implant 200 so that it is thinnest at theposterior surface 260 of the implant 200. The taper is preferably curvedand provides a convex configuration for a better anatomical fit, whilealso facilitating insertion of the implant 200 into the affected discspace. The PLIF implant 200 may have a height at its anterior surface ofabout 7 mm to about 17 mm and a height at its posterior surface of about4.6 mm to about 13.7 mm. Alternatively, the height of the PLIF implant200 may remain substantially constant throughout the implant 200. Theheight of the PLIF implant 200 preferably does not taper or change alongthe shorter axis 202 of the PLIF implant 200. Thus for any given crosssection taken perpendicular to the longitudinal axis 201 of the PLIFimplant 200, the distance between the upper and lower surfaces 300, 320remains substantially constant. Alternatively, the height of the PLIFimplant 200 may change or taper along the shorter axis 202 as well. Asgenerally shown and described in U.S. Pat. No. 6,986,788 entitledIntervertebral Allograft Spacer; U.S. Pat. No. 6,554,863 entitledIntervertebral Allograft Spacer, U.S. Pat. No. RE 38,614 entitledIntervertebral Allograft Spacer, U.S. patent application Ser. No.11/150,584 entitled Intervertebral Allograft Spacer and U.S. patentapplication Ser. No. 11/150,608 entitled Intervertebral AllograftSpacer, the entire contents of which are all expressly incorporated byreference, the PLIF implant is preferably sized and configured forinsertion in-between adjacent vertebra via a PLIF procedure whichgenerally involves insertion of two PLIF implants via a posteriorapproach, on either side of a midline of the spine, to the affectedintervertebral disk space.

One exemplary surgical technique for the PLIF procedure begins with thepatient being placed in a prone position on a lumbar frame. Next,radiographic equipment may be used to assist the surgeon in locating theprecise intraoperative position for the PLIF implant. Next, an incisionmay be made and the patient's skin may be dissected from the midlinelaterally. Following incision, the spinous process, lamina, dura, nerveroots, and other anatomical landmarks are identified. The affectedvertebrae are then preferably distracted using a lamina spreader or alateral distractor, both of which are commonly known in the art. Thesurgeon may then perform a lam inotomy to the medial aspect of the facetand reflects dura to expose a small window (e.g. approximately 13 mm) tothe disc space. Next a discectomy may be performed during whichsubstantially all of, and more preferably all, of the disc material fromthe affected disc space may be removed through the window. After thediscectomy is complete, the superficial layers of the entirecartilaginous endplates may be removed. This is done to expose bleedingbone, but care should be taken to avoid excess removal of subchondralbone, as this may weaken the anterior column. Entire removal of theendplate may result in subsidence and loss of segmental stability.

Next, an appropriately sized trial-fit PLIF spacer may be inserted intothe intervertebral disc space using gentle impaction, to determine theappropriate height of the PLIF implant for the disc space to be filled.Fluoroscopy can assist in confirming the fit of the trial spacer. Uponidentifying and removing the best fitting trial spacer, a PLIF implantof appropriate size is selected.

At this time, prior to placement of the PLIF implant, bone graftmaterial, such as autogenous cancellous bone or a bone substitute, maybe placed in the anterior and lateral aspects of the affected discspace. Moreover, since the PLIF implant is preferably formed with athrough bore, bone graft material may be inserted into the through-bore.Alternatively, the PLIF implant may come pre-arrived with bone graftmaterial packed therein.

During insertion, the PLIF implant may be held securely using a surgicalinstrument such as an implant holder, which may engage the channels orslots formed on the PLIF implant. The first PLIF implant may then beintroduced into the intervertebral disc space.

Regardless of which side of the spinous process the implant is insertedin, autogenous cancellous bone or a bone substitute should be placed inthe anterior and medial aspect of the vertebral disc space prior toplacement of the second PLIF implant. The distractor may then be removedand a second PLIF implant of the same height as the first PLIF implantmay be inserted into the space, using gentle impaction as before.Preferably, the implants are recessed 2-4 mm beyond the posterior rim ofthe vertebral body.

Alternatively, it should be noted that the T-PLIF and PLIF implants maybe inserted using minimally invasive procedures.

Referring back to FIGS. 6A-6J, an exemplary method for manufacturing amulti-piece allograft implant will now be described and shown inconnection with the T-PLIF implant. However, it should be understoodthat the PLIF implant may be similarly manufactured.

The members, such as, for example, the first and second members 50, 80or the first, second and third members 130, 135, 140, of the implant maybe individually formed (e.g. machined, sized, shaped, etc.) beforeassembling the T-PLIF implant. The individual members may be firstroughly shaped on the pre-selected bone 150, which may have beenobtained, for example, from a cadaver. The individual members of theimplant may be oriented such that the Haversian canals of each boneportion 150 may be substantially aligned to be roughly perpendicular tothe upper and lower surfaces of the implant. This orientation of thebone portions 150 may provide an implant having maximum strength in thevertical direction. This orientation of the bone portions 150 may alsoprovide the benefit of readily allowing blood and/or osteogenicmaterials to flow through the canals between the vertebral end plates,thus facilitating fusion of the implant with the adjacent vertebrae.

After forming the individual members into their desired shapes, thedesired shape including forming one of either the recess or projectionportion of a dovetail joint, the individual members may be removedand/or dislodged from the pre-selected bone 150. Next, the individualmembers may be assembled by sliding together, via the dovetail joint, tocreate the implant as shown in FIGS. 6D-J.

Next, one or more holes may be formed in the implant. The holes beingsized and configured to receive one or more pins. Alternatively, theholes may be formed before the individual members have been assembledinto the implant.

Alternatively and/or in addition, one or more through bores may beformed in the implant. The through bores being sized and configured toreceive bone graft material for facilitating spinal fusion.Alternatively, the bores may be formed before the individual membershave been assembled into the implant.

Moreover, after assembling, the projections and/or teeth may be formedinto the upper and lower surfaces of the implant. Alternatively, theteeth may be formed into the upper and lower surfaces of the implantbefore assembly. Additionally, one or more channels may be formed forreceiving the implant holder. This step may also occur before or afterassembling the implant.

By forming the individual members of the implant before assembling theimplant, in particular by shaping the outer shape or surface (e.g.perimeter) of the implant into the base tissue and then joining themembers of the intervertebral implant, the following advantages may beachieved. First, individually forming the individual members may allowfor a larger material footprint. This may be especially important whenforming implants from allograft bone due to limitations of materialthicknesses in available base allograft tissue. Second, the individualmachining of the dovetail geometry permits one to better control therequired complex tool path. For example, by individually forming themembers the user has better control over forming and/or shaping theouter shape or surface (e.g. perimeter) of the implant and the curveddovetail joint. Thus, individually forming the members prior to assemblymay result in greater size potential of the graft and better controlover forming the complex, geometries of the implant and dovetailfeature.

As will be appreciated by those skilled in the art, any or all of thecomponents described herein such as, for example, individual members,pins, etc. may be provided in sets or kits so that the surgeon mayselect various combinations of components to perform a fixationprocedure which is configured specifically for the particularneeds/anatomy of a patient. It should be noted that one or more of eachcomponent may be provided in a kit or set. In some kits or sets, thesame component may be provided in different shapes and/or sizes.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be understood that variousadditions, modifications, combinations and/or substitutions may be madetherein without departing from the spirit and scope of the invention asdefined in the accompanying claims. In particular, it will be clear tothose skilled in the art that the invention may be embodied in otherspecific forms, structures, arrangements, proportions, and with otherelements, materials, and components, without departing from the spiritor essential characteristics thereof. One skilled in the art willappreciate that the invention may be used with many modifications ofstructure, arrangement, proportions, materials, and components, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the invention. Inaddition, features described herein may be used singularly or incombination with other features. The presently disclosed embodiments aretherefore to be considered in all respects as illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims, and not limited to the foregoing.

What is claimed is:
 1. An allograft intervertebral implant sized andconfigured for implantation between first and second adjacent vertebra,the implant comprising: an allograft body formed from at least twopieces of allograft bone, the allograft body including a front surface,a back surface, a pair of ends separating the front and back surfaces,and an upper surface and a lower surface sized and configured forcontacting at least a portion of the first and second vertebrae, whereinthe front surface, the back surface, and the pair of ends define anouter perimeter of the implant; wherein the first allograft bone piecehas a first interface surface comprising a first portion of at least onedovetail joint, wherein the second allograft bone piece has a secondinterface surface comprising a second portion of the at least onedovetail joint, and wherein the at least two pieces of allograft boneare joined together by the at least one dovetail joint, the at least onedovetail joint being sized and configured to substantially follow theouter perimeter of the implant, and the at least one dovetail jointbeing sized and configured to achieve a press-fit type connection oncethe first and second portions of the at least one dovetail joint arefully joined together thereby providing resistance against separation ofthe at least two pieces of allograft bone.
 2. The allograft implant ofclaim 1, wherein the at least two pieces of allograft bone each includea hole at least partially formed therein, the hole being sized andconfigured to receive at least one pin for further securing the at leasttwo pieces of allograft bone together.
 3. The allograft implant of claim2, wherein the holes extend from the upper surface to the lower surface.4. The allograft implant of claim 2 further comprising the at least onepin, wherein the at least one pin intersects the first and secondinterface surfaces at an angle.
 5. The allograft implant of claim 4,wherein the angle is ninety degrees.
 6. The allograft implant of claim 1further comprising at least one channel sized and configured to engage asurgical instrument.
 7. The allograft implant of claim 1 furthercomprising at least one channel on the front surface, the back surface,or both surfaces and extending from one of the pair of ends.
 8. Theallograft implant of claim 1, wherein a height of the implant isgreatest at a midsection between the pair of ends and tapers graduallyalong a longitudinal axis.
 9. The allograft implant of claim 1, whereinthe front and back surfaces are curved.
 10. The allograft implant ofclaim 9, wherein the at least one dovetail joint has a curved shape thatsubstantially follows the contours of the curved front and back surfacesof the body.
 11. The allograft implant of claim 1, wherein the firstportion of the at least one dovetail joint comprises a recess and thesecond portion of the at least one dovetail joint comprises aprojection, and the recess becomes more narrow towards a rear of thedovetail joint proximate one of the pair of ends such that the at leastone dovetail joint becomes tighter once the projection is fully insertedinto the recess.
 12. The allograft implant of claim 11, wherein theprojection comprises two outwardly tapered side surfaces extending froma base surface to a substantially planar surface.
 13. The allograftimplant of claim 12, wherein a cross sectional area of the projection islarger as the distance of the projection from the base surfaceincreases.
 14. The allograft implant of claim 11, wherein the recesscomprises a base surface and two inwardly tapered side surfacesextending from the base surface.
 15. The allograft implant of claim 14,wherein a cross sectional area of the recess is smaller as the distanceof the recess from the base surface increases.
 16. The allograft implantof claim 11, wherein the recess is inwardly tapered and the projectionis outwardly tapered.
 17. The allograft implant of claim 1, wherein thefirst and second interface surfaces are configured to be substantiallyhorizontal when the upper surface, the lower surface, or both surfacesare substantially horizontal.
 18. The allograft implant of claim 1,wherein the allograft body is formed from at least three pieces ofallograft bone and each of the at least three pieces of allograft boneare joined together by the at least one dovetail joint.
 19. Theallograft implant of claim 1, wherein at least one of the upper surfaceand the lower surface include a plurality of teeth formed thereon. 20.The allograft implant of claim 1, further comprising at least onevertical through-bore extending from the upper surface to the lowersurface, the vertical through-bore being about half the length of thefront surface or longer and configured to receive bone graft material.